Every day, plant material is brought into the UK from abroad, providing flowers for our gardens, wood for our furniture and food for our tables. But what happens when this plant material has undetected insect hitchhikers?
Introductions of non-native insect species into the UK has become a regular occurrence as humans have advanced with international transport and trade. Each year, insect species are found here which have been historically absent, imported from Europe or further afield. Once these insects have arrived, climate change and ornamental planting mean that they are increasingly able to survive and breed.
It is important that we keep track of these non-native species as some have the potential to become pests. This usually happens when natural enemies such as predators, parasites and pathogens which would control species numbers in their native range are absent in the UK. The resultant freedom from these constraints can allow populations of a non-native insects to expand very quickly.
Invasive species pose a range of threats to wild and cultivated UK organisms. They can damage populations of native species by predating upon them and competing with them for food sources. An example of this is the invasive harlequin ladybird, which has become one of the most common ladybirds in the UK since its introduction from Asia in 2004. Its massive population increase has been linked to shrinking numbers of the small, native two-spot ladybird.
Non-natives can also threaten UK agriculture and forestry industries by bringing in new diseases or damaging crops through feeding. The Colorado potato beetle is so devastating to potato crops that, during the cold war, the East German government suspected American war planes might have been deliberately dropping them onto fields in Germany to destabilise food supply.
A key focus of the work of the SRI is in monitoring and supporting rare invertebrate conservation. However, sometimes when we are out surveying for rare species, we also make some surprising discoveries. While conducting a survey at the Queen Elizabeth Olympic Park as part of the Park’s Biodiversity Action Plan target monitoring, the SRI’s Stuart Connop and Caroline Nash had an unexpected encounter with a recently introduced beetle species. In May last year, they found a population of striking, red and blue leaf beetles. These were feeding on ornamentally planted purple willow trees and had caused extensive damage. Some of the trees looked very much worse for wear with only shredded remains of leaves attached.
The colourful beetles were identified as Chrysomela saliceti, a species with a wide natural range covering Europe and parts of Asia. Chyrsomela saliceti had been first recorded in the UK in 2012 when a population was found in the Cambridgeshire Fens and, since then, it has been found in few other British locations. However, C. saliceti looks very similar to its UK native relative, the Poplar Leaf Beetle (Chrysomela populi), meaning that it could be flying under the radar, spreading undetected around Britain.
A few months previously, another sighting of C. saliceti had been recorded from a different London location, The London Wetlands centre in Barnes. It is possible that both of these locations could have been supplied with members of the same stock of infested trees. Alternatively, this could be evidence that the beetle species is spreading throughout London.
As C. saliceti obviously has the potential to damage some species of willow tree, its future spread needs to be monitored. To help alert the community of UK beetle specialists, we have recently published an article in ‘The Coleopterist’ journal, where many new beetle sightings are publicised.
At a time when ambitious tree planting regimes are being fulfilled by plants imported from the continent, it is important that we keep a close eye out for new insect species coming in. Many of these will likely pose no threat to UK species; however, some have the potential to become invasive and could cause unprecedented problems. It is vital that these are noticed before it becomes too late.